1. Field of the Invention
The present invention relates to a control method effective for controlling a control object which rarely has static characteristics because it is a large-scale system or includes non-linearity, or a control object which cannot be well controlled by the conventional controller such as voltage/reactive-power of a power system, an automatically moving robot, a large-scale industrial plant, a rotating machinery e.g. a generator, an automatically navigator of a ship etc. or jets of fuel in an internal combustion engine etc., for example.
2. Description of the Prior Art
FIG. 1 is a conceptual diagram showing a typical control technique adopted by the conventional voltage/reactive-power controller described in Report 946 with the title "Development of a Voltage/Reactive-Power Controller" disclosed by M. Suzuki et al. in a national convention of the Society of Electrical Engineers of Japan which was held in the year of 1987. Reference numeral 18 shown in the figure is a dead zone in the central area of coordinate axes whereas reference numerals 19 each denote an operation-changeover line extended from the dead zone 18 in one of the four directions.
Next, the principle of operation of the conventional voltage/reactive-power controller is described. A voltage/reactive-power controller adopting the conventional control technique has a control plane with a pattern approximating the characteristics of a power system which are established with relations among the primary and secondary voltages V.sub.1 and V.sub.2 and the primary reactive power Q.sub.1 of its transformer used as a base. The voltage/reactive-power controller sustains the primary and secondary voltages V.sub.1 and V.sub.2 and the primary reactive power Q.sub.1 of the transformer at their target values by moving the tap of the load tap-changer up and down or controlling the input switching of a shunt reactor (SHR) and a synchronous condenser (SC) serving as a phase adjuster based on the pattern on the control plane shown in FIG. 1.
Since the conventional control technique is implemented as described above, the control characteristics are much affected by the pattern on the control plane set in the controller. It is difficult, on the other hand, to properly set a pattern on the control plane. It is therefore hard to give satisfactory control characteristics. In addition, since the effect of moving the tap up and down and controlling the input switching of the shunt reactor (SHR) and the synchronous condenser (SC) is not smooth, the conventional control technique gives rise to a problem that hunting or the like may result if the dead zone 18 is not set properly.